When propagating in a gas, acoustic waves will enable propagation medium gas to generate fluctuations of pressure, displacement, and temperature. When interacting with a fixed boundary, the gas can induce exchanges between acoustic energy and heat energy, which is thermoacoustic effect.
A thermoacoustic system is an energy conversion system designed using the thermoacoustic effect principle, which may convert heat energy into acoustic energy, or convert acoustic energy into heat energy. Thermoacoustic systems can be divided into two kinds: thermoacoustic engines and a thermoacoustic refrigerators, wherein thermoacoustic engines mainly includes traveling-wave thermoacoustic engines and Stirling engines, and thermoacoustic refrigerators mainly include traveling-wave thermoacoustic refrigerators, pulse tube refrigerators and Stirling refrigerators.
In the above thermoacoustic systems, the thermoacoustic engines and refrigerators are using air or inert gases, such as helium or nitrogen, as a working medium. They have advantages in high efficiency, safety and long service life, thus having attracted widespread public attention. Hitherto employing a thermoacoustic engine in power generation and employing a thermoacoustic refrigerator in low-temperature refrigeration have already been successful.
Refer to FIG. 1 being a schematic view of an existing traveling-wave thermoacoustic refrigeration system.
As it is shown in FIG. 1, the traveling-wave thermoacoustic refrigeration system includes three elementary units, where each elementary unit includes a linear motor 1a and a thermoacoustic conversion device 2a. 
The linear motor 1a includes a cylinder 11a, a piston 12a, a piston rod 13a, a motor housing 14a, a stator 15a, a mover 16a, and an Oxford spring 17a. 
The stator 15a and the inner wall of the motor housing 14a are fixedly connected; the mover 16a and the stator 15a are of clearance fit; the piston rod 13a and the mover 16a are fixedly connected; the piston rod 13a and the Oxford spring 17a are fixedly connected; when the linear motor 1a is working, the mover 16a drives the piston 12a performing a linear reciprocating motion within the cylinder 11a through the piston rod 13a. 
The thermoacoustic conversion device 2a includes a main heat exchanger 21a, a heat regenerator 22a, and a non-normal-temperature heat exchanger 23a connected in sequence. The main heat exchanger 21a is connected to a cylinder cavity of a linear motor 1a, i.e., a compression chamber 18a; the non-normal-temperature heat exchanger 23a is connected to a cylinder cavity of another linear motor 1a, i.e., an expansion chamber 19a; each thermoacoustic conversion device 2a is coupled to each linear motor 1a in sequence, thus, the thermoacoustic refrigerator constitutes a loop of medium flow.
When the traveling-wave thermoacoustic refrigeration system is working, electric power is supplied to the linear motor 1a. The mover 16a drives the piston 12a performing a linear reciprocating motion within the cylinder 11a, the gas medium volume within the compression chamber 18a has changed, generates acoustic energy and enters into the main heat exchanger 21a, passes through the heat regenerator 22a, within which most of the acoustic energy has been consumed, producing refrigeration effect so as to lower the temperature of the non-normal-temperature heat exchanger. The remaining acoustic energy once again comes out from the non-normal-temperature heat exchanger 23a, feeds back to an expansion chamber 19a of another linear motor 1a, and is transferred to a piston 12a of the second linear motor 1a. 
During the course of study for the present invention, the inventor has figured out technical limitations as follows: the traveling-wave thermoacoustic refrigeration system converts the electric power into acoustic power through the linear motor 1a, and realizes thermoacoustic energy conversion through the thermoacoustic conversion device 2a, producing refrigeration effect. Nevertheless, in an area with absence of electricity and abundant thermal energy, e.g., in an area where solar power is relatively adequate whereas electricity supply is inconvenient and electricity is scarce, the application of the existing travel-wave thermoacoustic refrigeration system will be largely restricted, even cannot be applied.
In addition, in the work of the traveling-wave thermoacoustic refrigeration system, since the temperature of the gas medium coming out from the non-normal-temperature heat exchanger 23a connected to the heat regenerator 22a is relatively lower, and the temperature of the gas medium fed back to the expansion chamber 19a is relatively lower, under the condition that the cylinder 11a and the piston 12a works in a relatively low temperature, there is high demand for the process and manufacture of the piston 12a. Therefore, the manufacturing cost of the traveling-wave thermoacoustic refrigeration system will be increased, and the service life of the linear motor 1a will be reduced.